Electrical connectors are known which have a plurality of terminals disposed in a dielectric housing and which are to be terminated to a respective plurality of conductor wires In one such connector the terminals are disposed in a single row within a housing molded thereover and extend rearwardly from the housing, to conclude in termination sections comprising shallow channels termed solder tails The housing may include cylindrical portions extending rearwardly to surround the terminals forwardly of the solder tails. When the conductor wires are prepared to be terminated to the solder tails, individual sleeve-like solder preforms encased within respective longer sleeves of heat recoverable or heat shrink tubing are placed over the rearwardly extending terminal portions so that the solder preforms surround the solder tails, or a strip of such units appropriately spaced apart; the stripped wire ends are then inserted into the heat recoverable tubing sleeves and into the solder preforms surrounding the solder tails; the entire assembly is then placed in a conventional thermal energy source and heated by convection, with the heat energy penetrating through the heat recoverable tubing to melt the solder which then flows around the stripped wire ends within the solder tails and upon cooling forms respective solder joints joining the conductor wires to the terminals; and simultaneously the heat recoverable tubing is heated above a threshold temperature at which the tubing shrinks in diameter until it lies adjacent and tightly against surfaces of the solder tails and the wire termination therewithin, a portion of the insulated conductor wire extending rearwardly therefrom, and a portion of the terminal extending forwardly therefrom to the rearward housing surface, sealing the exposed metal surfaces Apparatus for wire and sleeve handling with respect to such a connector is known such as from U S. Pat. No. 3,945,114. Within forward and rearward ends of the tubing are located short sleeve-like preforms of fusible sealant material which will shrink and also tackify upon heating to bond and seal to the insulation of the wire, and to the cylindrical housing portions therewithin and to bond to the surrounding heat recoverable tubing Examples of such assemblies of heat recoverable tubing lengths with solder preforms and sealant preforms therein are disclosed in U.S. Pat. Nos. 3,525,799; 4,341,921 and 4,595,724.
Conventional thermal energy sources achieve a temperature in excess of a control temperature, which is chosen to be somewhat above the ideal temperature at which a particular solder material melts in order to compensate for less than ideal thermal energy transfer. Several disadvantages attend such a thermal energy delivery method: portions of the connector other than connection sites are subjected to substantial heat which may be detrimental to the connector material; the thermal energy applied to connector portions other than the connection sites is wasted; components possibly may be damaged because of general overheating, and some sites may achieve a temperature much higher than necessary in order to assure that other sites achieve a sufficient solder melting temperature; the thermal energy source either requires a long warm-up period which is wasteful of time, or remains heated at its steady state temperature which is wasteful of energy; and maintenance of a continuous and accurate control over temperature and time is an ideal desire requiring a diligence and responsive apparatus not consistently met or found in practice. Another disadvantage is that heat recoverable tubing which is initially made transparent and is desired to remain transparent to allow visual inspection of the solder joint after termination, commonly receives enough excess thermal energy to opaquify, at least obscuring the solder joint therewithin.
It is known in the prior art to utilize a self-regulating temperature source which when energized by a constant amplitude, high frequency alternating current passing therethrough, generates thermal energy and achieves a resulting constant temperature. Such a temperature can be selected to be just higher than the ideal temperature at which solder melts. The self-regulating temperature source is disclosed in U.S. Pat. Nos. 4,256,945; 4,623,401; 4,659,912; 4,695,713; 4,701,587; 4,717,814; 4,745,264 and European Patent Publication No. 0241,597, which are expressly incorporated herein by reference. The self-regulating temperature source employs a substrate of copper or copper alloy or other conductive material of low electrical resistivity, negligible magnetic permeability and high thermal conductivity; deposited on one surface thereof is a thin layer of thermally conductive magnetic material such as iron, nickel or a nickel-iron alloy having a much higher electrical resistance and magnetic permeability than the substrate material.
When a radio frequency current for example is passed through such a two-layer structure, the current initially is concentrated in the thin high resistance magnetic material layer which causes heating; when the temperature in the magnetic material layer reaches its Curie temperature, it is known that the magnetic permeability of the layer decreases dramatically; the current density profile then expands into the non-magnetic substrate of low resistivity. The thermal energy is then transmitted by conduction to adjacent structure such as wires and solder which act as thermal sinks; since the temperature at thermal sink locations does not rise to the magnetic material's Curie temperature as quickly as at non-sink locations, the current remains concentrated in those portions of the magnetic material layer adjacent the thermal sink locations and is distributed in the low resistance substrate at non-sink locations It is known that for a given frequency the self-regulating temperature source achieves and maintains a certain maximum temperature dependent on the particular magnetic material.
The conductive substrate can be copper having a magnetic permeability of about one and a resistivity of about 1.72 micro-ohms per centimeter The magnetic material may be for example a clad coating of nickel-iron alloy such as Alloy No. 42 (forty-two percent nickel, fifty-eight percent iron) or Alloy No. 42-6 (forty-two percent nickel, fifty-two percent iron, six percent chromium). Typical magnetic permeabilities for the magnetic layer range from fifty to about one thousand, and electrical resistivities normally range from twenty to ninety micro-ohms per centimeter as compared to 1.72 for copper; the magnetic material layer can have a Curie temperature selected to be from the range of between 200.degree. C. to 500.degree. C. The thickness of the magnetic material layer is typically one skin depth; the skin depth is proportional to the square root of the resistivity of the magnetic material, and is inversely proportional to the square root of the product of the magnetic permeability of the magnetic material and the frequency of the alternating current passing through the two-layer structure
U.S. Pat. No. 4,987,283 discloses a method for terminating and sealing a termination of electrical conductors employing self-regulating temperature source technology, whether the conductors be a conductor wire and a termination section of a terminal or a pair of conductor wires. A stripped wire end is placed along a solder tail of a terminal; a sleeve-like solder preform containing flux is disposed around the wire end and solder tail; the solder preform is contained within a length of heat recoverable tubing which extends axially to opposed tubing ends around the insulated wire portion and an insulated terminal portion; sealant preforms are disposed within the opposed tubing ends and around the insulated wire portion and insulated terminal portion; a heater means having a first layer of conductive nonmagnetic metal and a second layer of high resistance magnetic material is placed around the heat recoverable tubing length; a high frequency alternating current is induced in or transmitted to the heater means which then generates thermal energy; and the thermal energy is transmitted to the tubing and the solder and sealant preforms, melting the solder to terminate the wire to the terminal and melting and tackifying the sealant preforms to bond to the insulated wire and terminal portions and shrinking the tubing, thus forming a termination and sealing it simultaneously.
In one exemplary embodiment of Ser. No. U.S. Pat. No. 4,987,283 a terminal subassembly is formed by placing a plurality of terminals in a dielectric housing, such as by molding dielectric material around body sections of the terminals, and contact sections of the terminals are exposed along a mating face of the housing for eventual mating with corresponding contact sections of another connector. Termination sections of the terminals extend rearwardly from the housing to be terminated to individual conductor wires, and comprise preferably shallow channels. Sleeve-like preforms of solder with flux are disposed around the termination sections, with lengths of heat recoverably tubing around the solder preforms and extending forwardly over cylindrical housing flanges covering the terminals forwardly of the terminating sections, to the rear surface of the housing, and rearwardly a distance beyond the ends of the termination sections. End portions of the insulated wires extend into the rearward end of the heat recoverable tubing lengths so that the stripped ends of conductor wires are placed along the respective channels of the termination sections of the terminals and within the solder preforms. Sleeve-like preforms of sealant material are disposed within the forward and rearward tubing sections to melt and shrink, tackify and bond to the housing flanges and wire insulation respectively, and bond to the surrounding portions of heat recoverable tubing.
Then, in accordance with Ser. No. U.S. Pat. No. 4,987,283 a heater means is then placed in position across the termination region above and below the termination sections. The heater means may be a strap wrapped around the plurality of termination sections having the heat recoverable tubing sleeves thereover containing the solder preforms. The metal strap comprises a self-regulating temperature source and includes two layers of different metals: a first layer of electrically conductive, low resistivity, low magnetic permeability metal such as copper or copper alloy; and a second layer of metal having high resistivity and high magnetic permeability such as iron, nickel or nickel-iron alloy. A selected constant amplitude high frequency alternating current is generated by an appropriate apparatus which is transmitted to or induced in the strap. The current in the strap over a short length of time produces thermal energy which rises to a certain temperature selected to be slightly higher than needed to melt the solder preforms The thermal energy is transmitted to the solder preforms within the lengths of heat recoverable tubing around the respective termination sections thereby melting the solder which forms solder joints between the wires and the termination sections. The thermal energy also is transmitted to and begins to melt and shrink and tackify the sealant preforms and to shrink the surrounding heat recoverable tubing which reduces to conform to the outer surfaces of the structure therewithin including the insulated wire portion, the termination sections including the terminations, the shrunken sealant preforms and the housing flanges The terminations of the terminals to the wires are completed and the terminations and all exposed metal is sealed and the strap removed, completing the connector. The current may be induced in the strap by an appropriate apparatus having a coil surrounding the strap which is disposed around the termination region transverse to the assembly, and the coil then being energized.
There is disclosed in U.S. Pat. No. 4,852,252 the use of terminal solder tails which have a layer of magnetic material clad onto an outer surface. When a stripped wire end is disposed along the inner surface of the solder tail and heat recoverable tubing assembly is placed thereover, and radio frequency current is induced in the solder tail by reason of the magnetic material, the heat melts the solder preform within the tubing to solder the wire end to the solder tail; simultaneously the sealant preforms are melted and seal the termination.
It is desired to obtain solder joints without heating all portions of the connector.
It is desired to consistently obtain assured solder joints in a multiterminal connector having prehoused terminals.
It is desired to provide a simple and convenient method for soldering and sealing a termination.
It is desired to provide a simple and convenient method for soldering and sealing a termination of a stripped wire end to a solder tail of a conventional terminal.